US6350815B1

US6350815B1 - Golf ball cover compositions

Info

Publication number: US6350815B1
Application number: US09/634,412
Authority: US
Inventors: Michael J. Sullivan; Robert A. Weiss
Original assignee: Top Flite Golf Co
Current assignee: Topgolf Callaway Brands Corp
Priority date: 1994-12-20
Filing date: 2000-08-08
Publication date: 2002-02-26
Anticipated expiration: 2014-12-20
Also published as: US5542677A; US6100336A; US5591803A

Abstract

The present invention is directed to golf ball cover compositions containing blends of high or low carboxylic acid based copolymers and ethylene copolymers such as ethylene alkyl acrylates. The carboxylic acid groups of the blends are neutralized with metal cations. Golf balls produced with the cover molded thereon exhibit desired properties of distance and high coefficient of restitution without substantially sacrificing and/or improving characteristics like playability and durability when compared to existing covers comprising ionomeric resin blends.

Description

This application is a continuation of application Ser. No. 08/661,608, filed Jun. 11, 1996, now U.S. Pat. No. 6,100,336, which is a continuation of U.S. application Ser. No. 08/551,254, filed on Oct. 31, 1995, now U.S. Pat. No. 5,591,803, which is a continuation of U.S. application Ser. No. 08/359,620, filed Dec. 20, 1994, now U.S. Pat. No. 5,542,677.

FIELD OF THE INVENTION

The present invention relates to metal cation neutralized blends of acid copolymers with non-acid functional polymers such as ethylene acrylates, and to improved golf ball covers made from these blends. The improved golf ball covers are useful for producing golf balls, particularly multi-piece balls, exhibiting essentially the desired travel distance while maintaining or improving the playability and/or durability characteristics necessary for repetitive play.

BACKGROUND OF THE INVENTION

Ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability, and flight characteristics, various ionomeric resins sold by E. I. DuPont de Nemours & Company under the trademark “Surlyn®” and more recently, by the Exxon Corporation (see U.S. Pat. No. 4,911,451) under the trademarks “Escor®” and the tradename “Iotek”, have become the materials of choice for the construction of golf ball covers over the traditional “balata” (trans polyisoprene, natural or synthetic) rubbers. The softer balata covers, although exhibiting enhanced playability properties, lack the durability properties required for repetitive play.

Ionomeric resins are generally ionic copolymers of an olefin, such as ethylene, and a metal salt of an unsaturated carboxylic acid, such as acrylic acid, methacrylic acid or maleic acid. In some instances, an additional softening comonomer can also be included to form a terpolymer. The pendent ionic groups in the ionomeric resins interact to form ion-rich aggregates contained in a non-polar polymer matrix. The metal ions, such as sodium, zinc, magnesium, lithium, potassium, calcium, etc. are used to neutralize some portion of the acid groups in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e. improved durability, etc. for golf ball construction over balata.

Broadly, the ionic copolymers comprise one or more alpha-olefins and from about 9 to about 30 weight percent of alpha, beta-ethylenically unsaturated mono- or dicarboxylic acid, the basic copolymer neutralized with metal ions to the extent desired. Usually, at least 20% of the carboxylic acid groups of the copolymer are neutralized by the metal ions (such as sodium, potassium, manganese, zinc, lithium, calcium, nickel, magnesium, and the like) and exist in the ionic state. In general, ionic copolymers including up to 16% acid are considered “low acid” ionomers, while those including greater than 16% acid are considered “high acid” ionomers by the present inventors.

Suitable olefins for use in preparing the ionomeric resins include ethylene, propylene, butene-1, hexene-1, and the like. Unsaturated carboxylic acids include acrylic, methacrylic, ethacrylic, α-chloroacrylic, crotonic, maleic, fumaric, itaconic acids, and the like. The ionomeric resins utilized in the golf ball industry are generally copolymers of ethylene with acrylic (i.e. Escor®) and/or methacrylic (i.e. Surlyn®) acid. In addition, two or more types of ionomeric resins may be blended into the cover compositions in order to produce the desired properties of the resulting golf balls.

Along this line, the properties of the cover compositions and/or the ionomeric resins utilized in the golf ball industry vary according to the type and amount of the metal cation, the molecular weight, the composition of the base resin (i.e. the nature and the relative content of the olefin, the unsaturated carboxylic acid groups, etc.), the amount of acid, the degree of neutralization and whether additional ingredients such as reinforcement agents or additives are utilized. Consequently, the properties of the ionomer resins can be controlled and varied in order to produce golf balls having different playing characteristics, such as differences in hardness, playability (i.e. spin, feel, click, etc.), durability (i.e. impact and/or cut resistance), and resilience (i.e. coefficient of restitution).

However, while there are currently more than fifty commercial grades of ionomers available from DuPont and Exxon with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (i.e. relative content of ethylene and methacrylic and/or acrylic acid groups), the degree of neutralization and additive ingredients such as reinforcement agents, etc., a great deal of research continues in order to develop golf ball cover compositions exhibiting not only the playability characteristics previously associated with the balata cover, but also the improved impact resistance and carrying distance properties produced by the ionomeric resins. Thus, an object of the present invention is to provide golf ball cover compositions which, when utilized in golf ball construction, produce balls exhibiting improved travel distance while maintaining satisfactory playability and durability properties such as coefficient of restitution (C.O.R.).

A golf ball's coefficient of restitution (C.O.R.) is the ratio of the relative velocity of the ball after direct impact to that before impact. One way to measure the coefficient of restitution is to propel a ball at a given speed against a hard massive surface, and measure its incoming velocity and outgoing velocity. The coefficient of restitution is defined as the ratio of the outgoing velocity to incoming velocity of a rebounding ball and is expressed as a decimal. As a result, the coefficient of restitution can vary from zero to one, with one being equivalent to an elastic collision and zero being equivalent to an inelastic collision.

The coefficient of restitution of a one-piece golf ball is a function of the ball's composition. In a two-piece or a multi-layered golf ball, the coefficient of restitution is a function of the core, the cover and any additional layer. While there are no United States Golf Association (U.S.G.A.) limitations on the coefficient of restitution values of a golf ball, the U.S.G.A. requires that the golf ball cannot exceed an initial velocity of 255 feet/second. As a result, golf ball manufacturers generally seek to maximize the coefficient of restitution of a ball without violating the velocity limitation.

In various attempts to produce a high coefficient of restitution golf ball exhibiting the enhanced travel distance desired, the golfing industry has blended various ionomeric resins. However, many of these blends do not exhibit the durability and playability characteristics necessary for repetitive play and/or the enhanced travel distance desired.

It is, therefore, desirable to develop golf ball cover compositions which produce golf balls exhibiting properties of desired carrying distance (i.e., possess desirable coefficient of restitution values) over known ionomeric cover blends such as those set forth in U.S. Pat. Nos. 4,884,814 and 4,911,451, without sacrificing or improving playability and/or durability characteristics.

Furthermore, while as stated above, Surlyn® and Escor® (i.e. “Iotek”) are materials of choice for golf ball cover construction when balata is not used, these materials are relatively costly. It has, therefore, become desirable to develop a low cost alternative to Surlyn® and Iotek (Escor®) ionomeric resins in golf ball cover construction while at the same time maintaining properties such as good coefficient of restitution (C.O.R.), softness, as well as the durability required for repetitive play.

These and other objects and features of the invention will be apparent from the following description and from the claims.

SUMMARY OF THE INVENTION

The present invention is directed to golf ball covers, and more particularly to golf ball cover compositions which comprise blends of high or low acid copolymers with ethylene alkyl acrylates. The golf ball covers of the invention provide a desirable low cost alternative to the Surlyn® and Iotek ionomeric resins so frequently used in golf ball cover construction when balata is not used.

The present invention is particularly directed to golf ball cover compositions which are prepared by blending an acid copolymer which contains about 1% to about 25% acrylic acid, such as an ethylene acrylic acid (EAA) copolymer, with an ethylene copolymer including up to about 30% by weight of an alkyl acrylate. The alkyl acrylate in the ethylene copolymer may be selected from among ethyl acrylate, methyl acrylate, butyl acrylate, or others. The ethylene copolymer may, therefore, comprise among others ethylene ethyl acrylate (EEA), ethylene methyl acrylate (EMA), and/or ethylene butyl acrylate (EBA). The blending step is followed by the addition of a cation or cation blend for neutralization.

The selection of type and ratio of the ethylene acrylic acid (EAA) copolymer to the ethylene alkyl acrylate (i.e., EEA, EBA, EMA, etc.) is based on the desired final hardness and spin rate of the ball. Preferably, the blend of the acid copolymer with the non-acid functional ethylene alkyl acrylate includes about 30 to 90 parts by weight acid copolymer, and about 10 to 70 parts by weight ethylene alkyl acrylate. More preferably, the blend is comprised of about 40 to 50 parts by weight acid copolymer and about 50 to 60 parts by weight ethylene alkyl acrylate. Most preferably the blend consists of about 50 to about 70 parts by weight acid copolymer and about 30 to 50 parts by weight ethylene alkyl acrylate.

In another aspect, the invention relates to a metal cation neutralized ionomer resin comprising a blend of i) a copolymer of about 1 weight percent to about 25 weight percent, preferably greater than 16 weight percent of an alpha, beta-unsaturated carboxylic acid (preferably acrylic acid) and an olefin (preferably ethylene), and ii) an ethylene alkyl acrylate. Approximately, 10t to about 90% of the carboxyl groups of the acid copolymer are neutralized with a metal cation such as a metal cation selected from the group consisting of manganese, lithium, potassium, calcium, maganese, zinc, sodium, and nickel.

In a further aspect, the present invention concerns a metal cation neutralized high acid ionomer resin comprising a blend of i) a copolymer consisting of about 17 to 25 percent by weight acrylic acid with the remainder, or balance, thereof being ethylene and ii) an ethylene alkyl acrylate. Approximately, 10% to 90% of the carboxyl groups of the acid copolymer are neutralized with a metal cation such as a metal cation selected from the group consisting of manganese, lithium, potassium, zinc, sodium, magnesium, calcium, and nickel.

In another further aspect, the invention relates to a golf ball comprising a core and a cover, wherein the cover is comprised of a blend of i) a copolymer of about 20% by weight of an acrylic acid and the remainder ethylene and ii) an ethylene alkyl acrylate, of which 10% to 90% of the carboxyl groups of the acrylic acid/ethylene copolymer are neutralized with a metal cation such as a metal cation selected from the group consisting of manganese, lithium, potassium, sodium, zinc, magnesium, calcium and nickel. In addition, the cover may contain one or more additional ingredients such as pigments, dyes, U.V. absorbers and optical brighteners. The core is generally a solid core.

Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the development of golf ball covers, and more particularly to golf ball cover compositions which comprise blends of ethylene copolymers (i.e., ethylene alkyl acrylates) with acid copolymers. These blends may be reacted with a neutralizing compound such as magnesium oxide, zinc oxide, zinc acetate, etc. In this regard, a golf ball cover having good durability, playability (spin) and C.O.R. at a low cost relative to Surlyn® or Iotek is provided.

The acid copolymer used herein may contain anywhere from 1 to 25 percent by weight and, it is preferable to utilize a high acid copolymer (i.e. a copolymer containing greater than 16% by weight acid, preferably from about 17 to about 25 weight percent acid, and more preferably about 20 weight percent acid). The acid copolymer is blended with the ethylene alkyl acrylate and the blend is neutralized with a metal cation salt capable of ionizing or neutralizing the copolymer to the extent desired (i.e. from about 10% to 90%).

The base acid copolymer is preferably made up of greater than 16% by weight of an alpha, beta-unsaturated carboxylic acid and an alpha-olefin. Optionally, a softening comonomer can be included in the copolymer. Generally, the alpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene, and the unsaturated carboxylic acid is a carboxylic acid having from about 3 to 8 carbons. Examples of such acids include acrylic acid, methacrylic acid, ethacrylic acid, chloroacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, with acrylic acid being preferred.

The softening comonomer that can be optionally included in the invention may be selected from the group consisting of vinyl esters of aliphatic carboxylic acids wherein the acids have 2 to 10 carbon atoms and vinyl ethers wherein the alkyl groups contain 1 to 10 carbon atoms.

Consequently, examples of a number of copolymers suitable for use in the invention include, but are not limited to, high acid embodiments of an ethylene/acrylic acid copolymer, an ethylene/methacrylic acid copolymer, an ethylene/itaconic acid copolymer, an ethylene/maleic acid copolymer, an ethylene/methacrylic acid/vinyl acetate copolymer, an ethylene/acrylic acid/vinyl alcohol copolymer, etc. The base copolymer broadly contains greater than 16% by weight unsaturated carboxylic acid, from about 30 to about 83% by weight ethylene and from 0 to about 40% by weight of a softening comonomer. More preferably, the copolymer contains about 20% by weight unsaturated carboxylic acid and about 80% by weight ethylene. Most preferably, the copolymer contains about 20% acrylic acid with the remainder being ethylene.

Along these lines, examples of the preferred high acid base copolymers which fulfill the criteria set forth above, are a series of ethylene-acrylic acid copolymers which are commercially available from The Dow Chemical Company, Midland, Mich., under the “Primacor” designation. These high acid base copolymers exhibit the typical properties set forth below in Table 1.

TABLE 1

Typical Properties of Primacor
Ethylene-Acrylic Acid Copolymers

			MELT	TENSILE	FLEXURAL	VICAT
	PERCENT	DENSITY,	INDEX,	YD. ST	MODULUS	SOFT PT	SHORE D
GRADE	ACID	glcc	g/10 min	(psi)	(psi)	(° C.)	HARDNESS

ASTM		D-792	D-1238	D-638	D-790	D-1525	D-2240
5980	20.0	0.958	300.0	—	4800	43	50
5990	20.0	0.955	1300.0	650	2600	40	42
5990	20.0	0.955	1300.0	650	3200	40	42
5981	20.0	0.960	300.0	900	3200	46	48
5983	20.0	0.958	500.0	850	3100	44	45
5991	20.0	0.953	2600.0	635	2600	38	40

¹The Melt Index values are obtained according to ASTM D-1238, at 190° C.

Due to the high molecular weight of the Primacor 5981 grade of the ethylene-acrylic acid copolymer, this copolymer is the more preferred grade utilized in the invention.

Other acid copolymers which may be used include an ethylene-methacrylic acid copolymer such as Nucrel® available from E. I. DuPont de Nemours & Co. Nucrel® is an ethylene copolymer which is inherently flexible like EVA copolymers, and which offers desirable performance characteristics similar to those of Surlyn® ionomers.

The Nucrel® acid copolymers are produced by reacting ethylene and methacrylic acid in the presence of free radical initiators. A branched, random ethylene methacrylic acid (EMAA) copolymer is produced thereby. Carboxyl groups are distributed along the chain and interact with carboxyl groups on adjacent molecules to form a weakly crosslinked network through hydrogen bonding. The carboxyl groups disrupt the linearity of the polyethylene.

Nucrel® ethylene copolymers offer tensile strength as high as 25 MPa (3,600 psi) and good performance at low temperatures (945 k J/m²at −40° C.). Properties of selected Nucrel® ethylene copolymers are listed in Table 2.

TABLE 2

TYPICAL PROPERTIES OF NUCREL ® ETHYLENE COPOLYMER RESINS

			NUC-	NUC-	NUC-	NUC-	NUC-	NUC-	NUC-	NUC-	NUC-	NUC-
			REL ®	REL ®	REL ®	REL ®	REL ®	REL ®	REL ®	REL ®	REL ®	REL ®
PROPERTY	UNITS	ASTM	010	035	403	410	535	599	699	714	925	960

Melt Index	dg/min	D1238	11	35	3.0	10	35	500	88	14	21	60
Density	g/cm³	D792	.934	0.94	.934	.933	.934	.918	.937	.937	0.97	.941
Tensile	MPa(kpsi)	D638	22.1	17.9	24.7	21.4	21.4	10.3	15.2	22.7	25	21.4
Strength			(3.2)	(2.6)	(3.6)	(3.1)	(3.1)	(1.5)	(2.2)	(3.3)	(3.6)	(3.1)
Elongation	%	D638	630	640	568	600	580	530	560	560	520	540
Flexural	MPa(kpsi)	D790
Modulus
23° C.			40.0	59	152	93.8	71	64.8	68.3	66.9	74	55.1
(73° F.)	(5.8)	(8.6)	(22)	(13.6)	(10.3)	(9.4)	(9.9)	(9.7)	(10.8)	(8.0)
Hardness	Shore D	D2240	40	40	53	49	48	42	46	50	50	46
Vicat	° C.	D1525,	64	60	83	80	75	65	71	74	67	62
Softening	(° F.)	Rate B	(147)	(140)	(181)	(176)	(167)	(149)	(160)	(165)	(153)	(144)
Temperature
Notched Izod	J/m (ft-lb/in)	256	NB¹	374 (7)	NB	NB	NB	NB	NB	NB	801	NB
											(15)
Tensile	kJ/m²(ft-lb/in²)	1822S
Impact
23° C.			998	1,060	756	872	723	413	491	812	755	606
2 (73° F.)			(475)	(SOS)	(360)	(41S)	(344)	(196)	(233)	(386)	(360)	(289)
−40° C.			647	945	442	707	486	55	288	465	275	342
(−40° F.)			(308)	(450)	(210)	(336)	(231)	(26)	(137)	(221)	(130)	(163)

NB¹= No Break

The cover may comprise about 30-90 percent by weight of an acid copolymer, preferably about 40-80 percent, and most preferably 50-70 percent acid copolymers. At the same time, the cover may comprise about 10-70 percent by weight of an ethylene copolymer, preferably 20-60 percent, and most preferably 30-50 percent ethylene copolymer.

Ethylene copolymers which may be used herein include ethylene-ethyl acrylate (EEA), ethylene-methyl acrylate (EMA), and ethylene-butyl acrylate copolymers. Ethylene-ethyl acrylate is made by the polymerization of ethylene units with randomly distributed ethylene acrylate (EA) comonomer groups. The ethylene-ethyl acrylate copolymers contain up to about 30% by weight of ethylene acrylate. They are tough, flexible products having a relatively high molecular weight. They have good flexural fatigue and low temperature properties (down to −65° C.). In addition, EEA resists environmental stress cracking as well as ultraviolet radiation.

Examples of ethylene-ethyl acrylate which may be used herein include Bakelite® DPD-6169 or Bakelite® DPD-6182 available from Union Carbide. Properties of these and other suitable ethylene-ethyl acrylate copolymers include:

TABLE 3

TYPICAL PROPERTIES OF UNION CARBIDE
ETHYLENE-ETHYL ACRYLATE

	TEST	DPD-	DPD-	DPD-
PROPERTY	METHOD	6169	6182	9169

Melt Index, g/10 minutes	D 1238	6	1.5	20
Density, g/cm³	D 1505	0.931	0.930	0.931
Flexural Modulus, psi^(a)	D 790	9,500	13,000	9,000
Secant Modulus of	D 638	5,000	6,200	4,300
Elasticity, psi^(a)
Ultimate Elongation, %^(a)	D 638	700	700	750
Tensile strength, psi^(a)	D 638	1,600	2,100	700
Yield Strength, psi^(b)	D 638	550	700
Bent Strip Stress	D 1693	>500	<1,000	350
Cracking Resistance,
100% “Igepel” Solvent,
F₅₀, hours
Durometer Hardness,	D 676
“A”		88	87	86
“D”		32	32	31
Brittleness Index, 50%	D 746	−105	66
Failure, ° C.
Vicat Softening Point,	D 1525	64
° C.
Compression Set, 10	D 395	56
days at 23° C.,
% recovery

^(a)Determined on 0.075-inch compression molded plaques.
^(b)Determined on 0.075-inch compression molded plaques. Material has no true yield point. Value represents tensile strength at 50% elongation.

EEA is similar to ethylene vinyl acetate (EVA) in its density-property relationships and high-temperature resistance. In addition, like EVA, EEA is not resistant to aliphatic and aromatic hydrocarbons. For comparison purposes, some typical properties of ionomers as well as ethylene vinyl acetate and ethylene ethyl acrylate are provided below:

TABLE 4

TYPICAL PROPERTIES OF IONOMERS AND EEA

	Ionomer	EVA	EEA	UNITS

Specific gravity

0.93

0.93-0.95

0.93

Yield strength

2.2

1.3

1.05

10³lbf/in²

Tensil modules

28-40

11

6

10³lbf/in²

Usual form of fracture

tough

Vicat softening point	71	83	64	° C.
ASTM brittleness temperature	−100	−70	−100	° C.
Power Factor 10²Hz	0.0015	0.0024	0.001
Dielectric constant 10³Hz	2.5	2.8	2.8

Ethylene-methyl acrylate copolymers contain up to about 30% by weight of methyl acrylate and yield blown films having rubberlike limpness and high impact strength. These copolymers may be useful in coating and laminating applications as a result of their good adhesion to commonly used substrates. EMAs have good heat-seal characteristics.

Ethylene-methyl acrylate copolymers are manufactured by reacting, at high temperatures and pressures, methyl-acrylate monomers with ethylene and free radical initiators. Polymerization occurs such that the methyl acrylate forms random side chains on the polyethylene backbone. The acrylic functionality decreases resin crystallinity and increases polarity to enhance resin properties. The properties depend on molecular weight (determined by melt index) and percent crystallinity. Percent crystallinity is determined by comonomer incorporation. As the comonomer content increases, the film become softer, tougher, and easier to heat seal.

EMA films have low modulus (<10,000 psi), low melting points, and good impact strength. In addition, the EMA resins are highly polar, and as a result are compatible with olefinic and other polymers. They adhere well to many substrates including LDPE, LLDPE, and EVA.

Examples of ethylene-methyl acrylate which may be used in the golf ball cover compositions of the present invention include the Optema™ or Escor® EMA copolymer resins available from Exxon Chemical Company. The Optema™/Escor® EMA resins are thermally stable ethylene methyl acrylate resins which will accept up to 65% or more fillers and pigments without losing their properties. They are more thermally stable than EVAs and can be extruded or molded over a range of 275-625° F. (compared to an EVA limit of 450° F.). EMAs are generally not corrosive when compared to EVAs, EAAs and ionomers. Some of the typical properties associated with the various grades of Optema™ EMA resins are found in the following Table 5:

TABLE 5

										VICAT
	MELT			TENSILE	FLEXURAL			TENSILE		SOFTENING
	INDEX	METHYL	DENSITY	STRENGTH	MODULUS		HARDNESS	IMPACT @	ELONGA-	PT
	dg/min	ACRY-	g/cm³	psi (MPa)	psi (MPa)	MELTING	SHORE A/D	73° F. (23° C.)	TION	(10,000)
OPTEMA	(ASTM	LATE	(ASTM	(ASTM	(ASTM	POINT	(ASTM	(ASTM	% (ASTM	(ASTM
GRADE	D1238)	WT %	D1505)	D638)	D790)	° F. (° C.)	D2240)	D1822)	D638)	D1525)

TC 020	6.0	6.5	0.928	1700 (12)	17500	215 (102)	>90/45	170 (360)	>800	172 (78)
					(120)
TC 115	0.7	16.5	0.938	1900 (13)	8300 (57)	185 (85)	91/41	260 (550)	>800	149 (65)
TC 114	3.2	18.0	0.948	1700 (12)	7100 (49)	178 (81)	89/38	260 (570)	>800	133 (56)
TC 110	2.0	21.5	0.942	1600 (11)	5100 (3S)	167 (75)	86/36	270 (570)	>800	126 (52)
TC 111	2.0	21.5	0.944	1600 (11)	5100 (35)	167 (75)	86/36	270 (570)	>800	126 (52)
TC 120	6.0	20.	0.942	1600 (11)	5100 (35)	169 (76)	86/35	250 (520)	>800	117 (47)
TC 130	20.0	21.5	0.941	1300 (9)	4900 (34)	167 (75)	85/33	230 (480)	>800	109 (43)
TC 140	135.0	21.5	0.939	1200 (8)	4900 (34)	162 (72)	84/32	170 (360)	>800	97 (36)
TC 113	1.0	23.5	0.939	1600 (11)	3700 (26)	165 (74)	83/33	310 (650)	>800	122 (50)
TC 220	5.0	24.0	0.945	1300 (9)	3900 (27)	156 (69)	82/32	280 (580)	>800	109 (43)
TC 221	5.0	27.0	0.948	1100 (8)	2800 (19)	147 (64)	79/28	280 (590)	>800	102 (39)
DEVEL-
OPMEN-
TAL
GRADES
XS-11.04	6.0	6.0	0.933	1410	11,4000	225 (107)	90/35	170 (363)	1450	182 (84)
				(13.3)	(78.6)
XS-12.04	3.0	28.0	0.953	760 (5.0)	1210 (8.3)	145 (63)	70/17	—	1060	—
XS-13.04	135.0	20.	0.940	700 (4.8)	2800 (19)	171 (77)	82/25	—	1400	121 (50)

Certain developmental grades of Optema™ EMAs may be used in formulating the golf ball covers herein. These developmental grades of resins are designated “XS”. Pertinent properties of XS-11.04, 12.04 and 13.04 are set forth above in Table 5. Melt index and methyl acrylate content of these and certain others are set forth in the following Table 6:

TABLE 6

PROPERTIES OF OPTEMA ™ DEVELOPMENTAL EMA RESINS

		METHYLACRYLATE
OPTEMA/GRADE	MELT INDEX (dg/min)	CONTENT (%)

XS-53.04	0.7	15
XS-54.04	1.0	24
XS-34.14*	2.0	20
XS-12.04	3.0	28
XS-61.48	5.0	24
XS-55.48	5.0	28
XS-11.04	6.0	6
XS-13.04	135.0	20

*Slip and antiblock added.

Chevron Chemical Company's ethylene-butyl acrylate copolymer, EBAC™, is stable at high temperatures, and may be processed as high as 600° F. Typical properties (or average values) of certain EBAC™ copolymers are set forth below in Table 7.

TABLE 7

PROPERTIES OF ETHYLENE-BUTYL ACRYLATE COPOLYMERS (EBAC ™ )

			EBAC ™	EBAC ™	EBAC ™	EBAC ™	EBAC ™
			DS-	DS-	DS-	DS-	DS-
			1263-	1120-	1122-	1123-	1256-
PROPERTIES	UNITS	ASTM	70	70	70	70	70

Melt Flow	gms/10	D-1238	0.5	2.0	6.0	20	3.0
	min
Butyl	%	—	18	20	20	20	28.0
Acrylate
Content
Density	gm/cc	D-1505	0.927	0.927	0.927	0.927	0.927
Melting	° C.	—	91	90	87	88	74
Point
Vicat	° C.	D-1525	65	60	55	49	—
Softening
Point
Brittleness	° C.	D-746	<−76	<−75	21 −75	<−75	<−76
Temperature
Hardness
Shore A	—	D-2240	—	—	88	88	74
Shore D	—	D-2240	38	33	—	27	23
Flexural	psi	D-747	4000	—	—	3000	—
Stiffness
Tensile	psi	D-638	2000	1400	1100	680	760
Ultimate²
Tensile @	psi	D-638	1900	1400	1100	680	760
Break²
Elongation	%	D-638	810	900	850	620	950
a Point
Break²

¹Melt Flow testing of condition E, 190° C. and 2.16 kg weight.
²Tensile Properties determined with Type IV compression molded samples, 20″/min crosshead speed.

The metal cation salts utilized in the invention are those salts which provide the metal cations capable of neutralizing, to various extents, the carboxylic acid groups of the high acid copolymer. These include acetate, oxide or hydroxide salts of lithium, calcium, zinc, sodium, potassium, nickel, magnesium, and manganese.

Examples of such lithium ion sources are lithium hydroxide monohydrate, lithium hydroxide, lithium oxide and lithium acetate. Sources for the calcium ion include calcium hydroxide, calcium acetate and calcium oxide. Suitable zinc ion sources are zinc acetate dihydrate and zinc acetate, a blend of zinc oxide and acetic acid. Examples of sodium ion sources are sodium hydroxide and sodium acetate. Sources for the potassium ion include potassium hydroxide and potassium acetate. Suitable nickel ion sources are nickel acetate, nickel oxide and nickel hydroxide. Sources of magnesium include magnesium oxide, magnesium hydroxide, magnesium acetate. Sources of manganese include manganese acetate and manganese oxide.

The cover compositions of the invention are produced by reacting the blend of the acid copolymer and the ethylene alkyl acrylate with various amounts of the metal cation salts above the crystalline melting point of the copolymer, such as at a temperature from about 200° F. to about 500° F., preferably from about 250° F. to about 350° F. under high shear conditions at a pressure of from about 100 psi to 10,000 psi. Other well known blending techniques may also be used. The amount of metal cation salt utilized to produce the cover compositions is the quantity which provides a sufficient amount of the metal cations to neutralize the desired percentage of the carboxylic acid groups in the high acid copolymer. The extent of neutralization is generally from about 10% to about 90%.

Additional compatible additive materials may also be added to the compositions of the present invention, such as dyes (for example, Ultramarine Blue sold by Whitaker, Clark, and Daniels of South Painsfield, N.J.), and pigments, i.e. white pigments such as titanium dioxide (for example Unitane 0-110) zinc oxide, and zinc sulfate, as well as fluorescent pigments. As indicated in U.S. Pat. No. 4,884,814, the amount of pigment and/or dye used in conjunction with the polymeric cover composition depends on the particular base ionomer mixture utilized and the particular pigment and/or dye utilized. The concentration of the pigment in the polymeric cover composition can be from about 1% to about 10% as based on the weight of the base ionomer mixture. A more preferred range is from about 1% to about 5% as based on the weight of the base ionomer mixture. The most preferred range is from about 1% to about 3% as based on the weight of the base ionomer mixture. The most preferred pigment for use in accordance with this invention is titanium dioxide.

Moreover, since these are various hues of white, i.e. blue white, yellow white, etc., trace amounts of blue pigment may be added to the cover stock composition to impart a blue white appearance thereto. However, if different hues of the color white are desired, different pigments can be added to the cover composition at the amounts necessary to produce the color desired.

In addition, it is within the purview of this invention to add to the cover compositions of this invention compatible materials which do not affect the basic novel characteristics of the composition of this invention. Among such materials are antioxidants (i.e. Santonox R), antistatic agents, stabilizers and processing aids. The cover compositions of the present invention may also contain softening agents, such as plasticizers, etc., and reinforcing materials such as glass fibers and inorganic fillers, as long as the desired properties produced by the golf ball covers of the invention are not impaired.

Furthermore, optical brighteners, such as those disclosed in U.S. Pat. No. 4,679,795, may also be included in the cover composition of the invention. Examples of suitable optical brighteners which can be used in accordance with this invention are Unitex OB as sold by the Ciba-Geigy Chemical Company, Ardaley, N.Y. Unitex OB is thought to be 2, 5-Bis (5-tert-butyl-2-benzoxazoly) thiophene. Examples of other optical brighteners suitable for use in accordance with this invention are as follows: Leucopure EGM as sold by Sandoz, East Hanover, N.J. 07936. Leucopure EGM is thought to be 7-(2h-naphthol (1,2-d)-triazol-2yl) -3phenyl-coumarin. Phorwhite K-20G2 is sold by Mobay Chemical Corporation, P.O. Box 385, Union Metro Park, Union, N.J. 07083, and is thought to be a pyrazoline derivative, Eastobrite OB-1 as sold by Eastman Chemical Products, Inc. Kingsport, Tenn., is thought to be 4,4-Bis (- benzoxaczoly) stilbene. The above-mentioned Uvitex and Eastobrite OB-1 are preferred optical brighteners for use in accordance with this invention.

Moreover, since many optical brighteners are colored, the percentage of optical brighteners utilized must not be excessive in order to prevent the optical brightener from functioning as a pigment or dye in its own right.

The percentage of optical brighteners which can be used in accordance with this invention is from about 0.01% to about 0.5% as based on the weight of the polymer used as a cover stock. A more preferred range is from about 0.05% to about 0.25% with the most preferred range from about 0.10% to about 0.020% depending on the optical properties of the particular optical brightener used and the polymeric environment in which it is a part.

Generally, the additives are admixed with a ionomer to be used in the cover composition to provide a masterbatch (M.B.) of desired concentration and an amount of the masterbatch sufficient to provide the desired amounts of additive is then admixed with the copolymer blends.

The cover compositions of the present invention may be produced according to conventional melt blending procedures. In this regard, the above indicated high acid ionomeric resins are blended along with the masterbatch containing the desired additives in a Banbury type mixer, two-roll mill, or extruded prior to molding. The blended composition is then formed into slabs or pellets, etc. and maintained in such a state until molding is desired. Alternatively a simple dry blend of the pelletized or granulated resins and color masterbatch may be prepared and fed directly into the injection molding machine where homogenization occurs in the mixing section of the barrel prior to injection into the mold. If necessary, further additives such as an inorganic filler, etc., may be added and uniformly mixed before initiation of the molding process.

Moreover, golf balls of the present invention can be produced by molding processes currently well known in the golf ball art. Specifically, the golf balls can be produced by injection molding or compression molding the novel cover compositions about wound or solid molded cores to produce a golf ball having a diameter of about 1.680 inches or greater and weighing about 1.620 ounces. The standards for both the diameter and weight of the balls are established by the United States Golf Association (U.S.G.A.). Although both solid core and wound cores can be utilized in the present invention, as a result of their lower cost and superior performance, solid molded cores are preferred over wound cores.

Conventional solid cores are typically compression molded from a slug of uncured or lightly cured elastomer composition comprising a high cis content polybutadiene and a metal salt of an α, β, ethylenically unsaturated carboxylic acid such as zinc mono or diacrylate or methacrylate. To achieve higher coefficients of restitution in the core, the manufacturer may include a small amount of a metal oxide such as zinc oxide. In addition, larger amounts of metal oxide than those that are needed to achieve the desired coefficient may be included in order to increase the core weight so that the finished ball more closely approaches the U.S.G.A. upper weight limit of 1.620 ounces. Other materials may be used in the core composition including compatible rubbers or ionomers, and low molecular weight fatty acids such as stearic acid. Free radical initiator catalysts such as peroxides are admixed with the core composition so that on the application of heat and pressure, a complex curing or cross-linking reaction takes place.

The term “solid cores” as used herein refers not only to one piece cores but also to those cores having a separate solid layer beneath the cover and above the core as in U.S. Pat. No. 4,431,193, and other multilayer and/or non-wound cores (such as those described in U.S. Pat. No. 4,848,770).

Wound cores are generally produced by winding a very large elastic thread around a solid or liquid filled balloon center. The elastic thread is wound around the center to produce a finished core of about 1.4 to 1.6 inches in diameter, generally. Since the core material is not an integral part of the present invention, a detailed discussion concerning the specific types of core materials which may be utilized with the cover compositions of the invention are not specifically set forth herein. In this regard, the cover compositions of the invention may be used in conjunction with any standard golf ball core.

As indicated, the golf balls of the present invention may be produced by forming covers consisting of the compositions of the invention around cores by conventional molding processes. For example, in compression molding, the cover composition is formed via injection at about 380° F. to about 450° F. into smooth surfaced hemispherical shells which are then positioned around the core in a dimpled golf ball mold and subjected to compression molding at 200-300° F. for 2-10 minutes, followed by cooling at 50-70° F. for 2-10 minutes, to fuse the shells together to form an unitary ball. In addition, the golf balls may be produced by injection molding, wherein the cover composition is injected directly around the core placed in the center of a golf ball mold for a period of time at a mold temperature of from 50° F. to about 100° F. After molding the golf balls produced may undergo various further finishing steps such as buffing, painting, and marking as disclosed in U.S. Pat. No. 4,911,451.

The present invention is further illustrated by the following examples in which the parts of the specific ingredients are by weight (pbw). It is to be understood that the present invention is not limited to the examples, and various changes and modifications may be made in the invention without departing from the spirit and scope thereof.

EXAMPLES

By blending the ingredients set forth in the Tables below, a series of golf ball cover formulations were produced. Finished golf balls were prepared using the cover compositions of the present invention, controls and comparative cover compositions by positioning a solid preformed cross-linked polybutadiene core in an injection molding cavity in such a manner to permit the uniform injection of the selected cover composition over each core. Along this line, the cover formulations were injection molded at about 400° F. around identical solid type cores having a finished diameter of 1.545 inches to produce golf balls approximately 1.680 inches in diameter having a normal cover thickness of 0.0675 inches. All materials were molded under essentially identical conditions. The properties of coefficient of restitution (C.O.R.) of the molded and finished balls, Shore D hardness, cold crack resistance, spin rates, etc. for the cover compositions were then determined.

In conducting the comparative prior art testing, Escor® 4000/7030 and Escor® 900/8000 ionomers were utilized. In this regard, blends of Escor® 4000/7030 and Escor® 900/8000 (i.e. the subject of U.S. Pat. No. 4,911,451) are considered by the inventors to be generally among the best prior art cover compositions concerning ethylene-acrylic acid ionomer (low acid) blends.

The data for each example represents the average data for one dozen balls produced according to the desired manner. The properties for the Examples were measured according to the following parameters:

Coefficient of restitution (C.O.R.) was measured by firing the resulting golf ball in an air cannon at a velocity of 125 feet per second against a steel plate which is positioned 12 feet from the muzzle of the cannon. The rebound velocity was then measured. The rebound velocity was divided by the forward velocity to give the coefficient of restitution.

Shore hardness was measured in accordance with ASTM Test D-2240.

Cold cracking resistance was measured by firing balls from an air cannon, 5 blows at 165 feet/sec, after the balls had been conditioned for 24 hours at −10° F. After allowing the balls to equilibrate to room temperature the balls are inspected for cover cracking.

The spin rate of the golf ball was measured by striking the resulting golf balls with a pitching wedge or 9-iron wherein the club-head speed is about 80 feet per second and the ball is launched at an angle of 26 to 34 degrees with an initial velocity of about 110-115 feet per second. The spin rate was measured by observing the rotation of the ball in flight using stop action Strobe photography.

Example 1 Preparation of Acrylic Acid Based High Acid Ionomers

A number of new cation neutralized acrylic acid based high acid ionomer resins were prepared utilizing as the copolymer of an olefin and an alpha, beta-unsaturated carboxylic acid, a 20 weight percent acrylic acid/ethylene copolymer produced by The Dow Chemical Company, Midland, Mich. under the designation “Primacor 5981.” According to The Dow Chemical Company, Primacor 5981 has a melt index (at 190° C., 2150 g) of 300 g/10 min. The carboxylic acid groups present in the 20 weight percent acrylic acid/ethylene copolymer were neutralized to various weight percentages by a number of different metal cation salts resulting in the production of several new thermoplastic elastomers exhibiting enhanced properties for golf ball cover production. Due to differences in the nature of the cation salts, the amount of cation salts utilized, etc., the new high acid ionomer resins produced differed substantially in the extent of neutralization and in melt indices, as well as in resilience (i.e. C.O.R.) and hardness values.

For the purpose of determining the weight percent of neutralization of the carboxylic acid groups in the acrylic acid/ethylene copolymer after reacting with various cation salts, it was assumed that 1 mole of sodium (Na⁺), potassium (K⁺), and lithium (Li⁺) neutralized one mole of acrylic acid, and that one mole of zinc (Zn²⁺), magnesium (Mg²⁺), manganese (Mn²⁺), calcium (Ca²⁺) and nickel (Ni²⁺) neutralized two moles of acrylic acid. The calculations of neutralization were based upon an acrylic acid molecular weight of 79 g/m, giving 0.2778 moles per 100 grams of copolymer.

As indicated below in Table 8, the various cation salts were added in variable amounts to the 20 weight percent acrylic acid/ethylene copolymer in order to determine the optimal level of neutralization for each of the cations. In Table 8, NaOH refers to sodium hydroxide (formula weight of 40). MnAc refers to manganese acetate tetrahydrate having a formula weight of 245. LiOH is lithium hydroxide, fwt=24. KOH is potassium hydroxide, fwt=56. ZnAc is zinc acetate dihydrate, fwt=219.5. MgAc is magnesium acetate tetrahydrate, fwt=214.4. CaAc is calcium acetate, fwt=158. MgO is magnesium oxide, fwt=40.3. NiAc is nickel acetate, fwt=176.8. All of these cation salts are solids at room temperature.

The specific cation salts were added in differing amounts with the 20 weight percent acrylic acid/ethylene copolymer (i.e. the Primacor 5981) to an internal mixer (Banbury type) for the neutralization reaction. The only exception was calcium acetate, which, due to problems encountered in solid form, was added as a 30 wt-% solution in water.

In the neutralization reaction, the cation salts solubilized in the Primacor 5981 acrylic acid/ethylene copolymer above the melting point of the copolymer and a vigorous reaction took place with a great deal of foaming occurring as the cation reacted with the carboxylic acid groups of the acrylic acid/ethylene copolymer and the volatile by-products of water (in the case of oxides or hydroxides) or acetic acid (when acetates are used) were evaporated. The reaction was continued until foaming ceased (i.e. about 30-45 minutes at 250-350° F.), and the batch was removed from the Banbury mixer. Mixing continued, of the batch obtained from the mixer on a hot two-roll mill (175-250° F.) to complete the neutralization reaction. The extent of the reaction was monitored by measuring melt flow index according to ASTM D-1238-E. As indicated below, the neutralized products exhibited drastically different properties depending upon the nature and amount of the cation salts utilized.

TABLE 8

Formulation	Wt-%	Wt-%	Melt		Shore D
No.	Cation Salt	Neutralization	Index	C.O.R.	Hardness

1(NaOH)	6.98	67.5	0.9	.804	71
2(NaOH)	5.66	54.0	2.4	.808	73
3(NaOH)	3.84	35.9	12.2	.812	69

4(NaOH)

2.91

27.0

17.5

.812

(brittle)

5(MnAc)	19.6	71.7	7.5	.809	73
6(MnAc)	23.1	88.3	3.5	.814	77
7(MnAc)	15.3	53.0	7.5	.810	72

8(MnAc)

26.5

106

0.7

.813

(brittle)

9(LION)	4.54	71.3	0.6	.810	74
10(LiOH)	3.38	52.5	4.2	.818	72
11(LiOH)	2.34	35.9	18.6	.815	72

12(K0H)

5.30

36.0

19.3

Broke

70

13(KOH)	8.26	57.9	7.18	.804	70
14(KOH)	10.7	77.0	4.3	.801	67
15(ZnAc)	17.9	71.5	0.2	.806	71
16(ZnAc)	13.9	53.0	0.9	.797	69
17(ZnAc)	9.91	36.1	3.4	.793	67
18(MgAc)	17.4	70.7	2.8	.814	74
19(MgAc)	20.6	87.1	1.5	.815	76
20(MgAc)	13.8	53.8	4.1	.814	74
21(CaAc)	13.2	69.2	1.1	.813	74
22(CaAc)	7.12	34.9	10.1	.808	70
23(MgO)	2.91	53.5	2.5	.813
24(MgO)	3.85	71.5	2.6	.608
25(MgO)	4.76	89.3	1.1	.609
26(MgO)	1.96	35.7	7.5	.615
27(NiAc)	13.04	61.1	0.2	.602	71
28(NiAc)	10.71	46.9	0.5	.799	72
29(NiAc)	8.26	36.7	1.8	.796	69
30(NiAc)	5.66	24.4	7.5	.786	64

Controls:
50/50 Blend of Ioteks 8000/7030 C.O.R. = .810/65 Shore D Hardness
DuPont High Acid Surlyn ® 8422 (Na) C.O.R. = .811/70 Shore D Hardness
DuPont High Acid Surlyn ® 8162 (Zn) C.O.R. = .807/65 Shore D Hardness
Exxon High Acid Iotek EX-960 (Zn) C.O.R. = .796/65 Shore D Hardness
Control for Formulations 23-26 is 50/50 Iotek 8000/7030,
C.O.R. = .814, Formulation 26 C.O.R. was normalized to that control accordingly
Control for Formulation Nos. 27-30 is 50/50 Iotek 8000/7030, C.O.R. = .807

As indicated in Table 8, a number of the new cation neutralized acrylic acid based high acid ionomer resins exhibited C.O.R. and Shore D hardness values greater than that exhibited by a 50/50 blend of the Iotek low acid acrylic acid based hard ionomer resins, such as the Iotek 8000/7030 blend utilized in the cover compositions disclosed in U.S. Pat. No. 4,911,451. Moreover, included in new acrylic acid based high acid ionomer resins were numerous cation neutralized high acid ionomer resins previously not available, such as those acrylic acid based high acid ionomer resins neutralized to various degrees by the manganese, lithium, potassium, magnesium, calcium and nickel salts. Furthermore, the new cation neutralized acrylic acid based high acid ionomers produced C.O.R. and hardness values greater than those shown by the methacrylic acid based high acid ionomer resins recently produced by DuPont (i.e. Surlyn® 8422 (Na) and Surlyn® 8162 (Zn)) and the acrylic acid based high acid resins experimentally produced by Exxon (i.e. Iotek EX-959 and Ex-960 (Zn)), collectively referred to as “the controls.”

In addition, the results produced by Formulation Nos. 1 through 3 directed to the sodium ion neutralized ethylene-acrylic acid copolymers and Formulation Nos. 15 through 17 directed to the zinc ion neutralized ethylene-acrylic acid copolymers in comparison to the new Iotek high acid ethylene acrylic acid ionomers were also of interest. As indicated above, Escor® or Iotek Ex-959 is a sodium ion neutralized ethylene-acrylic acid copolymer and Escor® or Iotek Ex-960 is a zinc neutralized ethylene-acrylic acid copolymer. According to Exxon, Ioteks 959 and 960 contain from about 19.0 to about 21.0% by weight acrylic acid with approximately 30 to about 70 percent of the acid groups neutralized with sodium and zinc ions, respectfully.

Formulation No. 2 (i.e. 5.66 wt-% sodium salt, 54 wt-% neutralization, 2.4 melt index, 0.808 C.O.R. and 73 Shore D hardness) is somewhat similar to Iotek 959 and Formulation No. 16 (i.e. 13.9 wt-% zinc salt, 53 wt-% neutralization, 0.9 melt index, 0.797 C.O.R. and 69 Shore D hardness) is somewhat similar to Iotek 960.

However, not only did the new cation neutralized acrylic acid based high acid ionomers exhibit similar or better resilience (C.O.R.) at comparable or better hardness values than those exhibited by the sodium or zinc high acid Iotek ionomers, as a result of the neutralization of the acrylic acid/ethylene copolymer with several different cation salts, to a number of different neutralization percentages, a wide variety of new cation neutralized acrylic acid based high acid ionomers were produced having improved resilience and hardness values. These new cation neutralized high acid ionomer resins are particularly valuable in the field of golf ball production.

More particularly, the development of a number of separate different cation neutralized high acid ionomers besides the sodium or zinc high acid ionomers available from DuPont or Exxon, such as the new manganese, lithium, potassium, magnesium, calcium and nickel acrylic acid based high acid ionomer resins, allows for the production of a wide variety of cation neutralized high acid ionomer blends. Furthermore, since the new sodium or zinc neutralized high acid ionomers produced improved properties over those produced by the existing available sodium or zinc high acid ionomers, a number of new cover compositions can be produced having enhanced characteristics.

Along this line, several of the cation neutralized acrylic acid based high acid ionomer resins produced above which exhibited enhanced C.O.R. and Shore D hardness values were blended together and evaluated for the purpose of determining whether any synergistic effects were produced particularly with respect to enhanced C.O.R. values.

Specifically, from each group of the different cation neutralized high acid ionomer resins set forth in Table 8, the best overall ionomer (based upon C.O.R., melt index and Shore D hardness) was utilized to produce a number of blends (“diblends” and “triblends”) and processed to produce the cover component of multi-layered golf balls. The “diblends” consisted of 50/50 mixtures and the “triblends” consisted of a 33.33/33.33/33.33 mixtures.

With respect to the blends set forth below, Na refers to Formulation No. 3, C.O.R. (molded/finished) of 0.812/817; Mn refers to Formulation No. 6, C.O.R. (molded/finished) of 0.814/0.814; Li refers to Formulation No. 10, C.O.R. (molded/finished) of 0.818/0.819; K refers to Formulation No. 13, C.O.R. (molded/finished) of 0.805/0.809; Zn refers to Formulation No. 16, C.O.R. (molded/finished) of 0.797/0.796; Mg refers to Formulation No. 18, C.O.R. (molded/finished) of 0.814/0.820; Ca refers to Formulation No. 21, C.O.R. (molded/finished) of 0.813/0.812; Ni refers to Formulation No. 28, C.O.R. (molded/finished) of 0.799/0.817; and 50/50 Iotek 8000/7030 refers to control of 50/50 blend of Iotek 8000/7030, C.O.R. (molded/finished) of 0.810/0.812. The C.O.R. values of the “diblends” and “triblends” were then evaluated after molding with a center stock having the following composition:


	MATERIAL	WEIGHT (phr)

	BR-1220¹	70.70
	Taktene 220²	29.30
	React Rite ZDA³	31.14
	Zinc Oxide	6.23
	Zinc Stearate	20.15
	Limestone	17.58
	Ground Flash (20-40 mesh)	20.15
	Blue Masterbatch	.012
	Luperco 231XL⁴	.89
	or Trigonox 29/40⁵
	Papi 94⁶	.50

	¹BR-1220 is high cis-polybutadiene from Shell Chemical Co., Houston Texas.
	²Taktene is high cis-polybutadiene from Polysar Chemical.
	³ZDA is zinc diacrylate.
	⁴Luperco 231XL is a peroxide-free radical initiator manufactured and sold by Atochem, Buffalo, New York.
	⁵Trigonox 29/40 is peroxide-free radical initiator manufactured and sold by Akzo Chemie America, Chicago, Illinois.
	⁶Papi 94 is a polymeric diisocyanate available from Dow Chemical Co., Midland, Michigan.

In addition, the molded balls were coated and finished according to the procedure mentioned above. The C.O.R. values of the finished balls were determined in order to evaluate whether any improvement in resilience was produced. Generally, it is typical to observe a 0.002 to 0.003 point pick up in C.O.R. values of the finished balls in comparison to the molded balls. The results are set forth in Tables 9A, 9B and 10 below.

TABLE 9A

Diblends (50/50 Blends) C.O.R.
(Molded/Finished) Values

Formulation No.	Blend	C.O.R. (Molded/Finished)

31	Na/Mn	.813/.818
32	Na/Li	.813/.818
33	Na/K	.809/.816
34	Na/Zn	.811/.818
35	Na/Mg	.813/.819
36	Na/Ca	.811/.819
37	Mn/Li	.811/.817
38	Mn/K	.811/.818
39	Mn/Zn	.807/.814
40	Mn/Mg	.809/.816
41	Mn/Ca	.809/.816
42	Li/K	.810/.817
43	Li/Zn	.813/.819
44	Li/Mg	.812/.820
45	Li/Ca	.811/.818
46	K/Zn	.810/.815
47	K/Mg	.811/.820
48	K/Ca	.810/.817
49	Zn/Mg	.807/.814
50	Zn/Ca	.808/.814
51	Mg/Ca	.801/.818
52	Na/Ni	.809/.815
53	Mn/Ni	.807/.814
54	Li/Ni	.809/.816
55	K/Ni	.809/.816
56	Zn/Ni	.799/.804
57	Mg/Ni	.805/.813
58	Ca/Ni	.807/.815
59	Iotek 959/960	.811/.818
60	Control	.809/NA
61	Control	.806/NA

Controls are Formulation No. 59, a 50/50 blend of Iotek 959/960;
Formulation No. 60 a 75/25 blend of Surlyn 8162/8422; and
Formulation No. 61 a 50/50 blend of Iotek 8000/7030.

TABLE 9B

Synergy Values of the DiBlends

Formulation	Salt	Salt	(COR)	(COR)	(COR) exp-	Final	Final	Final
No.	1	2	calc	exp	(COR) calc	(COR) calc	(COR) exp	(COR) Diff.

31	Na	Mn	813.0	813.0	0.0	815.5	818.0	2.5
32	Na	Li	815.0	813.0	−2.0	818.0	818.0	0.0
33	Na	K	808.0	809.0	1.0	813.0	816.0	3.0
34	Na	Zn	804.5	811.0	6.5	806.5	818.0	11.5
35	Na	Mg	813.0	813.0	0.0	818.5	819.0	0.5
36	Na	Ca	812.5	811.0	−1.5	814.5	819.0	4.5
37	Mn	Li	816.0	811.0	−5.0	816.5	817.0	0.5
38	Mn	K	809.0	811.0	2.0	811.5	818.0	6.5
39	Mn	Zn	805.5	807.0	1.5	805.0	814.0	9.0
40	Mn	Mg	814.0	809.0	−5.0	817.0	816.0	−1.0
41	Mn	Ca	813.5	809.0	−4.5	813.0	816.0	3.0
42	Li	K	811.0	810.0	−1.0	814.0	817.0	3.0
43	Li	Zn	807.5	813.0	5.5	807.5	819.0	11.5
44	Li	Mg	816.0	812.0	−4.0	819.5	820.0	0.5
45	Li	Ca	815.5	811.0	−4.5	815.5	818.0	2.5
46	K	Zn	800.5	810.0	9.5	802.5	815.0	12.5
47	K	Mg	809.0	811.0	2.0	814.5	820.0	5.5
48	K	Ca	806.0	810.0	4.0	810.5	817.0	6.5
49	Zn	Mg	805.5	807.0	1.5	808.0	814.0	6.0
50	Zn	Ca	805.0	808.0	3.0	804.0	814.0	10.0
51	Mg	Ca	813.5	810.0	−3.5	816.0	818.0	2.0
52	Na	Ni	805.5	809.0	3.5	817.0	815.0	−2.0
53	Mn	Ni	806.5	807.0	0.5	815.5	814.0	−1.5
54	Li	Ni	808.5	809.0	0.5	818.0	816.0	−2.0
55	K	Ni	801.5	809.0	7.5	813.0	816.0	3.0
56	Zn	Ni	798.0	799.0	1.0	806.5	804.0	−2.5
57	Mg	Ni	806.5	805.0	−1.5	818.5	813.0	−5.5
58	Ca	Ni	806.0	807.0	1.0	814.5	815.0	0.5

In Table 9B above, the C.O.R. synergy values are based upon the data from Table 8 of the various metal cation neutralized high acid acrylic acid based ionomer resins and the following calculations:

(COR) calc=coefficient calculated as weighted average of as-molded COR's for polymers of salts 1 and 2

(COR) exp=experimental as-molded COR for blend

FINAL (COR) calc=coefficient calculated as weighted average of finished COR's for polymers of salts 1 and 2

FINAL (COR) exp=experimental finished COR for blend

FINAL (COR) diff=difference between FINAL (COR) exp and FINAL (COR) (calc)

As noted in Table 9B, positive synergy in resilience is observed for nearly all of the finished (final) blends, with substantial synergy being produced in Formulation Nos. 34, 38, 39, 43, 46, 48, 49, 50.

Moreover, the diblends were also evaluated against a control Formulation No. 59 (see Table 9A), a 50/50 blend of Iotek 959/960, the best available high acid blends, with respect to improved C.O.R. values (i.e. 811/0.818). Similar or enhanced C.O.R. values (molded/finished) were observed in Formulation Nos. 31 (Na/Mn), 32 (Na/Li), 34 (Na/Zn), 35 (Na/Mg), 36 (Na/Ca), 38 (Mn/K), 43 (Li/Zn), 44 (Li/Mg), 45 (Li/Ca), and 47 (K/Mg).

Furthermore, when reviewed for cold cracking, with the exception of Formulation No. 35, all of the diblends tested exhibited resistance to breaking. With respect to Formulation No. 35, some breakage did occur with 2 out of the 12 balls tested exhibiting breakage.

When the small test sample of the triblends were evaluated (see Table 10 below) in comparison to a 50/50 blends of the low acid acrylic acid based hard ionomers (i.e. Iotek 8000/7030 U.S. Pat. No. 4,911,451), all of the cation neutralized high acid acrylic acid based triblends produced enhanced C.O.R. values upon molding and finishing. In addition, when subjected to cold cracking, no breakages were observed.

TABLE 10

		C.O.R.	C.O.R.
Formulation	Cation Blend	Molded	Finished Ball

62	Zn/Li/K	.819	.828
63	Na/Zn/Li	.821	.829
64	Iotek 8000/7030	.816	.819
65	Na/Mn/Ca	.820	.828
66	Na/K/Mn	.821	.829
67	Na/K/Mg	.821	.829

Consequently, not only are a number of new cation neutralized acrylic acid based high acid ionomers now available for golf ball cover construction, these new cation neutralized acrylic acid based high acid ionomers may be blended together in various combinations to produce cover compositions exhibiting enhanced resilience (i.e. distance) due to the synergies noted above.

Example 2

In order to determine whether the diblends or triblends of the new cation neutralized acrylic acid based high acid ionomer resins produced different results when dry blended (i.e. prepared as simple dry blends of pre-made single cation neutralized acrylic acid based high acid ionomers, such as those set forth in Example 1 above) or when produced as “in-situ” cation blends (i.e. the cations were first blended and then added to the acrylic acid/ethylene copolymers in the Banbury mixer), a number of comparison reactions were generated. Specifically, in-situ Formulation Nos. 68-72 in Table 11 below correspond to dry-blended Formulation Nos. 31, 32, 43, 44 and 46, respectively, and in-situ Formulation Nos. 73 and 74 in Table 11 below correspond to dry-blended Formulation Nos. 62 and 63, respectively.

TABLE 11

				Spin Rate	Shore
Formulation		C.O.R	C.O.R.	9-Iron,	D Hard-
No.	Cation Blend	Molded	Finished	RPM	ness

68	Na/Mn	.822	.828	5,008	74
69	Na/Li	.820	.828	5,820	70
70	Li/Zn	.820	.825	5,425	71
71	Li/Mg	.821	.828	5,451	73
72	Zn/K	.817	.821	5,934	69
73	Li/Zn/K	.822	.826	5,266	71
74	Na/Li/Zn	.821	.824	5,165	71
75	Iotek	.819	.824	5,926
	959(Na)/
	960(Zn)
Tour Edition ®				10,124
100
Tour Edition ®				9,821
90
Top-Flite ®				6,942
XL II

The results indicated that little difference in C.O.R. was produced (relative to a control of 50/50 mixture of the high acid Iotek 959/960) whether a dry blending process or an in-situ blending process was used. Moreover, the data further clearly indicated that the cation neutralized acrylic acid based high acid ionomer blends of the present invention generally exhibit higher C.O.R. values and significantly lower spin rates than the best acrylic acid based high acid ionomers (i.e. the Ioteks 959(Na)/960(Zn) blend), see Formulation Nos. 68, 70, 71, 73 and 74 in comparison to Formulation No. 75 (control). The lower C.O.R. value and the substantially similar spin rate produced by the Zn/K blend in Formulation 72 was attributed to the slightly lower hardness of this blend versus the others. As indicated in Table 8, the K and Zn acrylic acid based high acid ionomers are a little softer than the Na, Mn, Li and Mg acrylic acid based high acid ionomers. Similarly, the higher spin rate of the Na/Li blend in Formulation 69 was due to its relative softness versus the other blends. In addition, other more subtle factors may also be at play, such as differences in coefficient of friction, deformation under load, etc., which have not quantified.

In addition, when compared with a number of commercially available balls produced by Spalding & Evenflo Companies, Inc., the assignee of the present invention, with low acid ionomer resin covers (i.e. the Tour Edition® 100, Tour Edition® 90 and Top-Flite® XL II balls), the spin rates of the cation neutralized acrylic acid high acid ionomer blends of the present invention (i.e. Formulations 68-75) exhibited much lower spin rates. Consequently, the cation neutralized acrylic acid based high acid ionomer blends of the present invention produced, when utilized to formulate the cover of a multi-layered golf ball, a much harder surface then those produced by the low acid ionomer covers presently available. This may be desirable to a golfer who imparts unmanageable spin (slice/hook) to the ball and therefore may benefit from a “low spin” ball.

Example 3 Acrylic Acid Based High Acid Ionomer Di-Blends Containing Varying Ratios of Cation Neutralized Acrylic Acid Based High Acid Ionomers

In addition to the 50/50 blends of various combinations of the new cation neutralized acrylic acid based high acid ionomers set forth in Example 1, di-blends varying from 25/75 to 75/25 ratios were produced utilizing the more preferred diblends in the “in-situ” process described in Example 2. In this regard, the more preferred diblend formulations set forth in Example 1 (i.e. Formulation No. 31 (Na/Mn), Formulation No. 32 (Na/Li), Formulation 43 (Li/Zn), Formulation No. 44 (Li/Mg), and Formulation No. 46 (Zn/K)) were produced in-situ in 50/50, 25/75 and 75/25 combinations according to the following formulations:

TABLE 12

Formulations

Ingredients	76	77	78	79	80	81	82	83	84	85

Acid	100	100	100	100	100	100	100	100	100	100
Copolymer
(Primacor
5981)
NaOH	2.0	1.0	3.0	2.0	1.0	3.0	—	—	—	—
Mn Acetate	15.0	22.5	7.5	—	—	—	—	—	—	—
Lithium	—	—	—	3.1	4.7	1.6	3.1	1.6	4.7	3.1
Hydroxide
Monohydrate
Zinc	—	—	—	—	—	—	8.00	12.0	4.0	—
Acetate
Potassium	—	—	—	—	—	—	—	—	—	—
Hydroxide
Magnesium	—	—	—	—	—	—	—	—	—	10.5
Acetate

Formulations No.

Ingredients	86	87	88	89	90

Primacor 5981	100	100	100	100	100
Lithium Hydroxide	1.6	4.7	—	—	—
Magnesium Acetate	15.8	5.3	—	—	—
Zinc Acetate	—	—	8.00	12.0	4.0
Potassium	—	—	4.50	2.25	6.75
Hydroxide

di-blends produced the following C.O.R. values:

TABLE 13

Formulation No.	Cation Blend	C.O.R. (Molded)

76	50/50 Na/Mn	.820
77	25/75 Na/Mn	.821
78	75/25 Na/Mn	.825
79	50/50 Na/Li	.822
80	25/75 Na/Li	.822
81	75/25 Na/Li	.823
82	50/50 Li/Zn	.816
83	25/75 Li/Zn	.804
84	75/25 Li/Zn	.825
85	50/50 Li/Mg	.823
86	25/75 Li/Mg	.822
87	75/25 Li/Mg	.821
88	50/50 Zn/K	.820
89	75/25 Zn/K	.798
90	25/75 Zn/K	.821

Control is a 50/50 Iotek Low Acid Ionomer Blend (8000/7030),
C.O.R. (molded) .817

The results indicated that in general the new cation neutralized acrylic acid based high acid ionomer diblends produced enhanced C.O.R. values over the known acrylic acid based low acid ionomer blends. See Formulation Nos. 76-81, 84-88 and 90. While Formulation 82 produced a lower C.O.R. value than expected, the data suggested that in some cases, a 50/50 blend is not optimal (particularly in the Zn/K and the Li/Zn blends), while in others (i.e. Li/Mg, Na/Li) the blend ratio is not significantly different.

Example 4

Since the data set forth in Examples 1-3 indicated the resilience (C.O.R.) and/or hardness properties of the cover compositions can be substantially enhanced through the use of the new cation neutralized acrylic acid based high acid ionomers and/or diblends or triblends of such ionomers, the molecular weight property of the acrylic acid/ethylene copolymers utilized to produce the ionomers was evaluated. Specifically, the molecular weight of the acid copolymers was assessed for the purpose of determining whether further enhanced properties can be produced by varying the molecular weight of the acid copolymer.

In this regard, since the data indicated that there was little difference between using the dry blending process or the in-situ blending method for processing the cations, the in-situ method of producing the cation neutralized high acid ionomer blends was used in this analysis.

Along this line, the diblend and triblends set forth in Formulation Nos. 68, 73 and 74 are essentially the same as those set forth below in Formulation Nos. 91, 94 and 97, respectively. However, since a different batch of cores was utilized than those used in Example 2, the C.O.R.'s are slightly lower. While the cores utilized in the present Example were of the same composition, the lower C.O.R. was due to the age of the cores, i.e. molded cores will lose C.O.R. upon aging mainly due to moisture pickup. Formulation Nos. 92-93, 95-96 and 98-99, are similar to those set forth in Formulation Nos. 91, 94 and 97, respectively, with the exception that the molecular weight of the acrylic acid/ethylene copolymer utilized was varied. Specifically, Primacor 5983 and Primacor 5990 both contain the same acid content as Primacor 5981 (i.e. 20 weight percent acrylic acid) but have lower viscosities (lower molecular weights) and lower densities. Primacor 5981 has a melt index of 300 g/10 minute (ASTM Method D-1238 at 190° C.) and a Brookfield viscosity of 51,000 cps at 350° F. Primacor 5983 has a melt index of 500 and a Brookfield viscosity of 26,000 cps at 350° F.; and Primacor 5990 has a melt index of 1300 and viscosity of 13,000 cps at 350° F.

The resilience (C.O.R.) of the molded balls produced utilizing the different molecular weight acrylic acid/ethylene copolymers are set forth below in Table 14.

TABLE 14

Formulation No.	Cations	Acid Copolymer	C.O.R. (MOLDED)

91	Na/Mn	Primacor 5981	.813
92	Na/Mn	Primacor 5983	.805
93	Na/Mn	Primacor 5990	All Balls crack
94	Li/Zn/K	Primacor 5981	.814
95	Li/Zn/K	Primacor 5983	.809
96	Li/Zn/K	Primacor 5990	All Balls crack
97	Na/Li/Zn	Primacor 5981	.813
98	Na/Li/Zn	Primacor 5983	.808
99	Na/Li/Zn	Primacor 5990	All Balls crack

The data indicated that a higher molecular weight acid copolymer is preferred for obtaining high resilience (i.e. C.O.R.) and required toughness.

Example 5

By way of further example, golf ball cover compositions were prepared by first blending an acid copolymer such as ethylene acrylic acid copolymer (EAA) with a non-acid functional polymer such as ethylene-ethyl acrylate (EEA) and/or ethylene-methyl acrylate (EMA). This was followed by addition of a cation or cation blend for neutralization. Selection of the type and ratio of acid copolymer to EEA or EMA was based upon the desired final properties of the ball such as hardness or spin rate. Tables 15-17 show the compositions and properties of balls having covers prepared using ethylene acrylates, and Table 18 shows the properties of several golf balls produced by the present assignee which do not contain ethylene acrylates but exhibit somewhat similar properties.

Table 15 below provides for the results of simple blends of ionomers with various non-acid functional polymers. Iotek's 959 and 960 were selected for their similarity in properties to ionomers made from Primacor 5981.

TABLE 15

Formulation
No.	100	101	102	103	104	105	106	107

Iotek 959	50	25	25	25	25	25	25	25
Iotek 960	50	25	25	25	25	25	25	25
Kraton	—	50	—	—	—	—	—	—
FG-1901X
EEA 6169	—	—	50	—	—	—	—	—
EEA 6182	—	—	—	50	—	—	—	—
EMA 53.04	—	—	—	—	50	—	—	—
EMA XS 12.04	—	—	—	—	—	50	—	—
EMA TC-130	—	—	—	—	—	—	50	—
Fusabond	—	—	—	—	—	—	—	50
D-197
Compression	56	59	61	60	61	61	63	60
Shore C Hard-	98	85	86	88	80	85	80	88
ness
Cut Resistance	4-5	3	2-3	2	2	2	2	2
Spin Rate	5,969	9,495	8,997	9,260	9,145	9,732	9,857	9,340
(full 9 iron)

*Several balls cracked on Formulations 101 and 106 during COR testing.

Blends similar to those of Table 15 were prepared using Primacor 5981 as the acid copolymer of choice instead of Iotek 959/960. These blends, and the resulting properties, are set forth below in Table 16:

TABLE 16

Formulation
No.	108	109	110	111	112	113	114	115

Primacor	100	50	50	50	50	50	50	50
5981
Nucrel 960	—	—	—	—	—	—	—	—
Kraton	—	50	—	—	—	—	—	—
FG-1901X
EEA 6169	—	—	50	—	—	—	—	—
EEA 6182	—	—	—	50	—	—	—	—
EMA 53.04	—	—	—	—	50	—	—	—
EMA	—	—	—	—	—	50	—	—
X512.04
EMA	—	—	—	—	—	—	50	—
TC-130
Fusabond	—	—	—	—	—	—	—	50
D-197
Zinc Acetate	5.33	5.33	5.33	5.33	5.33	5.33	5.33	5.33
Potassium	3.00	3.00	3.00	3.00	3.00	3.00	3.00	3.00
Hydroxide
Lithium	2.05	2.05	2.05	2.05	2.05	2.05	2.05	2.05
Hydroxide
Compression	55	62	60	60	63	63	62	62
Molded	.820	.802	.792	.794	.791	.790	.793	.802
COR
Finished	.825	.802	.792	.796	.793	.790	.794	.801
COR
Shore C	98	90	86	90	77	83	83	8.8
Hardness
Cut	4-5	3	3	3	2	3	2	3-4
Resistance
Spin Rate	5,787	8,834	9,232	9,148	10,220	9,516	9,552	9,091
(Full 9
Iron)

While Primacor 5981 has been the acid copolymer of choice herein as a result of its high COR, it should be noted that lower acid copolymers or a blend of acid copolymers may be used with satisfactory results. Table 17 below shows several compositions using lower acid copolymers or a blend of acid copolymers, along with the resulting properties of the finished cover and ball.

TABLE 17

Formulation
No.	116	117	118	119	120

Primacor	—	—	—	25	—
5981

Nucrel 960

50

25

100

Kraton	—	—	—	—	—
FG-1901X
EEA 6169	—	—	—	—	—

EEA 6182

50

—

EMA 53.04

—

50

—

50

—

EMA	—	—	—	—	—
X512.04
EMA	—	—	—	—	—
TC-130

Fusabond	—	—	50	—	—
D-197

Zinc Acetate	4.00	4.00	4.00	4.70	4.00
Potassium	2.27	2.27	2.27	2.60	2.27
Hydroxide
Lithium	1.50	1.50	1.50	1.80	1.50
Hydroxide
Compression	68	66	64	64	58
Molded	.793	.789	.800	.790	.813
COR
Finished	.793	.788	.798	.790	.815
COR
Shore C	86	75	88	76	96
Hardness
Cut	3	3	3	3	4
Resistance
Spin Rate	9,436	10,306	9,315	10,168	7,014
(Full 9 Iron)

One of the objectives in preparing the formulations listed in Tables 15-17 was to make a soft covered golfball having properties similar to the current “Tour” balls of the present assignee. The properties of the subject assignee's Titleist Tour 100, Tour Edition 100, Tour Edition 90, and Top-Flite XL II are provided in Table 18. These properties may be compared with those listed in Tables 15-17 to find many similarities such that a lower cost alternative may be provided.

TABLE 18

	Tour	Tour	Top-
Titleist	Edition	Edition	Flite XL
Tour 100	100	90	II

Compression

75

57

55

47

Molded COR

—

Finished COR	.786	.809	.813	.814
Shore C Hardness	82	84	86	96

Cut Resistance

1

3

4-5

Spin Rate (Full 9 Iron)	9,422	9,924	9,703	6,968

Little is known of the reaction mechanism or to what extent the EEA and/or EMA actually take part in the reaction of EEA/EMA with an acid copolymer and the addition of a cation or cation blend for neutralization. There is, however, some belief that there is at least enough interaction between polymers to provide a net benefit in properties versus a simple blend of an ionomer and EEA/EMA. It is possible that an interpenetrating polymer network (IPN) is formed by reacting (neutralizing) the acid copolymer in the presence of EEA/EMA. By first forming an intimate blend of polymers and then neutralizing one in the presence of another it is possible that a network is formed via intermolecular chain entanglement of the two polymers.

It is also possible that a dynamic vulcanization takes place where superior properties are the result of a finer phase morphology of the dispersed crosslinked phase (here, the neutralized acid copolymer) in an essentially uncrosslinked continuous matrix of ethylene acrylate ester.

The formations of Tables 15-17 above include examples of an acid copolymer reacted in the presence of maleic anhydride functional elastomers Kraton FG-1901X and Fusabond D-197. In simple blends with ionomers, this was the subject of U.S. Pat. Nos. 4,986,545 and 5,098,105, incorporated herein by reference.

A further advantage of the reactive blends of Tables 16 and 17 over the non-reactive blends of Table 15 is the improved cut resistance. While most of the blends of Table 15 give an undesirable “2” rating, nearly all of those in Tables 16 and 17 give a rating of “3”, which is comparable to the current Tour balls (see, e.g. Table 18). It should be further noted that formulations 101 and 106 in Table 15 had several balls break during COR testing. The related formulations in Table 16 (formulations 109 and 114) did not have this problem. In general, although no COR advantage is observed (i.e., some COR values of Table 16 are higher and some are lower than the corresponding Table 15 formulations) the balls prepared using the formulations of Table 16 are tougher, slightly softer and more durable than those of Table 15.

The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such alterations and modifications insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

We claim:

1. A golf ball having a core and a cover wherein said cover comprises about 30 to 90 parts by weight of a carboxylic acid/α-olefin copolymer wherein the carboxylic acid has from about 3 to 8 carbon atoms and the α-olefin has from about 2 to 10 carbon atoms and about 10 to 90% of carboxyl groups in the carboxylic acid are neutralized by a metal cation; and said cover further comprises about 10 to 70 parts by weight of an ethylene/alkyl acrylate copolymer which contains up to about 30% weight alkyl acrylate.

2. The golf ball as set forth in claim 1 wherein the carboxylic acid/α-olefin copolymer further comprises a softening comononer.

3. The golf ball as set forth in claim 2 wherein the softening comonomer is selected from the group consisting of vinyl esters of aliphatic carboxylic acids wherein the carboxylic acid has 2 to 10 carbon atoms and vinyl ethers having alkyl groups of 1 to 10 carbon atoms.

4. The golf ball, as set forth in claim 2, wherein the cover comprises about 40 to 80 parts by weight of the carboxylic acid/α-olefin copolymer and about 20 to 60 parts by weight of the ethylene/alkyl acrylate copolymer.

5. The golf ball, as set forth in claim 2, wherein the cover comprises about 50 to 70 parts by weight of the carboxylic acid/α-olefin copolymer and about 30 to 50 parts by weight of the ethylene/alkyl acrylate copolymer.

6. The golf ball, as set forth in claim 2, wherein the ethylene/alkyl acrylate copolymer is ethylene ethyl acrylate.

7. The golf ball, as set forth in claim 2, wherein the ethylene/alkyl acrylate copolymer is ethylene methyl acrylate.

8. The golf ball, as set forth in claim 2, wherein the ethylene/alkyl acrylate copolymer is ethylene butyl acrylate.

9. The golf ball, as set forth in claim 1, wherein the metal cation is selected from the group consisting of zinc, potassium, lithium, calcium, sodium, nickel, magnesium, and manganese.

10. A golf ball having a core and a cover wherein said cover comprises about 30 to 90 parts by weight of a carboxylic acid/α-olefin copolymer wherein the carboxylic acid has from about 3 to 8 carbon atoms and further comprises a softening comonomer and the α-olefin has from about 2 to 10 carbon atoms and about 10 to 90% of carboxyl groups in the carboxylic acid are neutralized by a metal cation; and said cover further comprises about 10 to 70 parts by weight of an ethylene/alkyl acrylate copolymer which contains up to about 30% weight alkyl acrylate.

11. The golf ball, as set forth in claim 10, wherein the metal cation is selected from the group consisting of zinc, potassium, lithium, calcium, sodium, nickel, magnesium, and manganese.

12. The golf ball as set forth in claim 11 wherein the softening comonomer is selected from the group consisting of vinyl esters of aliphatic carboxylic acids wherein the carboxylic acid has 2 to 10 carbon atoms and vinyl ethers having alkyl groups of 1 to 10 carbon atoms.

13. The golf ball, as set forth in claim 11, wherein the cover comprises about 40 to 80 parts by weight of the carboxylic acid/α-olefin copolymer and about 20 to 60 parts by weight of the ethylene/alkyl acrylate copolymer.

14. The golf ball, as set forth in claim 11, wherein the cover comprises about 50 to 70 parts by weight of the carboxylic acid/α-olefin copolymer and about 30 to 50 parts by weight of the ethylene/alkyl acrylate copolymer.

15. The golf ball, as set forth in claim 11, wherein the ethylene/alkyl acrylate copolymer is ethylene ethyl acrylate.

16. The golf ball, as set forth in claim 11, wherein the ethylene/alkyl acrylate copolymer is ethylene methyl acrylate.

17. The golf ball, as set forth in claim 11, wherein the ethylene/alkyl acrylate copolymer is ethylene butyl acrylate.

18. The golf ball, as set forth in claim 11, wherein the metal cation is selected from the group consisting of zinc, potassium, lithium, calcium, sodium, nickel, magnesium, and manganese.